Picture of How to Make a Spot Welder - for Cheap!!

Step 1: You Might Be Surprised How Cheap It Can Be

Picture of You Might Be Surprised How Cheap It Can Be
Have you seen the video above?  If not, take a look now because it will help you as you go along in this instructable. 

A typical resistance Spot-Welder can range in price from about $200-$800, but with a little resourcefulness, and a bit of free time, you can make one like this for about $10 or less.

Spot welders are used to fuse thin sheets of metal together.  They are most likely used in the auto industry, as well as HVAC for welding metal ducting.  

There are a couple of videos you should see before starting on this project, because you may want some background on how the device works.

Here is how to: Make The Metal Melter

Here is what it can do:  The Metal Melter
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Pondguy made it!3 days ago
This was a fun project. I was surprised at how well it worked. it has come in handy on a few projects.
JeffG23 months ago

Thanks for this project. I managed to bodge one together and to my surprise it actually works - a bit TOO well actually. So, I have a couple of questions:

1) I am using 4 AWG THHN wire and it's very stiff. is there any way to connect thinner gauge wire to the thick leads? I want to make some sort of hand piece or probes to get into tighter spots (as opposed to having these fixed in one place and maneuvering the pieces to be welded under it). Leads to my next question…

2) The heat created is too intense and actually melts the metal too quickly (I am creating armatures out of relatively thin garment hanger wire). Is there any way to attach a dimmer switch/potentiometer to this? And if so, will a regular household dimmer switch work or do I need something else?

Any answers and suggestions are greatly appreciated.

kweixelman made it!3 months ago
I wired in the light and use pallet wood total if 15$ spent.

Looks awesome

harry.godwin39 months ago

Anyone noticed we're trying to fit 6 inches of 2x2 into a 4.5 inches of space?

2x2s are 1.5"x1.5"

vshljn059446 months ago

Sir can you please tell the rating of transformer you used in this project

that is the input and output voltage rating and current required to generate the melting at the desired spot to melt

pandamopeds137 months ago
Whatisthe thickest metal this will tolerate? Again, another fantastic write up sir.
Charles511 year ago

I put one of these contraptions together using your video as a guide and those of several others on YouTube. Melts wire amazingly. As an artist I need to spot weld wire together to form armatures. The wire gets red hot and will melt but it does not weld together and comes apart when additional pieces are added. Any idea why?

Sounds like too much resistance in the wire. Have you tried using bigger wire? Also keep the wire run from the transformer as short as possible.

Possum Living7 months ago

Great instructable, Grant!

RobertP77 months ago

Hi, enjoy seeing what you have made. On the spot welder what wire are you using leading to the welding tips? 2/0 seems too stiff to have the arms removable or did I just miss something here?


Lots of projects I see I'm going to start doing in my retirement years!

fredF19 months ago

Are the transformer shunts left in or taken out?

The shunts are removed.

pnosko9 months ago

Let me ask a dumb question. You are using 1/4" hex screws to mount the terminal lugs to the arms. Considering that your metal melter videos show you melting similar screws, what is preventing these mounting screws from melting?

pnosko pnosko9 months ago

Answering my own question below after watching some educational electricity videos, I think the reason the 1/4" bolts are not affected is because the leads direct contact to the terminals make that the shortest path for the current, so it does not actually pass through the bolts.

Fission Chips10 months ago

Cool! I know this is dangerous to some extent, but exactly how dangerous is it?

felippec1 made it!12 months ago

I made it and work fine. thank you for inspiration.

Felippe Cardelino


SIRJAMES091 year ago

Sir, you never cease to amze me!

this is just too cool!!! :)

TY for sharing Sir.

stamatelos1 year ago

Thank you it is very usuful i will try to bild sun

I_StarkGuy made it!1 year ago

Finished mine! I changed the design to adapt it to available materials and I added the microwave fan to cool the MOT.

Can you weld galvanized steel? Mine is not able to do it, though my math gives me above 950 amps.


I think you can weld galvanized BUT the fumes given off are very toxic and potentially lethal. If you have to do this use a respirator, work outside or better yet, just try to avoid this if at all possible.

It is not that toxic in small quantities. And I work outside and I have been exposed to the fumes when melting screws.

The toxicity of galvanized metal when welded was one of the first lessons taught me by a pro. That said, just be careful (really, wear a respirator no matter where you are)!

JestGold1 year ago

Really like these projects and the metal melter/spot welder appear to be exactly what I need. Was wondering a couple of things:

a) I create metal sculptures from thin gauge wire rod and is there any way to regulate the amount of power so the metal fuses instead of melting (the spot welder seems to do just that)? and…

b) can the arms be separated or made into some sort of hand piece to make it more practical/accessible to the work?

Many thanks!

reddrexx1 year ago
I made one! But changed up the arms a bit. It works great.
14, 12:02 AM.jpg14, 12:02 AM.jpg
Are you sure you don't have AWG 2/0 wire ? It looks thicker than my AWG 2 wire. (2/0 is really 00 awg)
ccrow21 year ago
I have transformer from a die hard 6 and 12 volt battery charger I'm wondering how that would work, several input leads on the primary, the charger also had a 75 amp jump start setting also. Hmmm anybody wanna help me with where to start 6v 12v? I'd better do some math.
Pecheck1 year ago
late reply, but very awesome project. I'm definitely building one. I'll just ad a computer fan and some vent holes to by transformer housing.
kade1992 years ago
hey i was just wonder if for the MOT i should use the 2 AWG (since the 4 AWG melted) or if i should do the 8 gauge wire wrapped 16 times like in your arc welder video? which would be better overall for the spot welder?
I would think that if 8AWG wire wrapped 16 times worked better for the spot welder, then he probably would have said so, since they are both HIS videos ;-) But maybe he learned since making this one, and hasn't updated...
At any rate, 16 turns on the same core would result in higher voltage -- haven't watched the arc welder video yet -- guessing about 20V. Along with V increase, I (current, and resulting heat) goes down. I bet that the 2AWG (same number of turns) is the way to go here, since heating will occur in the secondary AND the work. I think the idea is to get the high current for the heat, and just make sure not to try melting anything that melts easier than the secondary's insulation! Assuming insulation was no issue, you'd simply have to keep the work easier to melt than the secondary itself, which is probably a complex relationship between relative masses and melting points.

But now I'm gonna have to go watch the arc welder video... are those capacitors I smell? :-)
GraphixS62 years ago
Do you know any place that you can reliably get dead microwaves. It seems my neighbors don't have a habit of just throwing them out.
f.masoni2 years ago
I love this project, i want to make one of my own but have a couple of questions.

Where i live the voltage of a power outlet is 220v does this change anything?

Also is it possible to make one that welds two separate spots at once with the same transformer.

Best Regards
calebwang2 years ago
I love your project. Your video editing is top notch as well.
The King of Random (author)  calebwang2 years ago
Thank you! Thank you!
Hi there. Thanks for this amazing project! I was amazed how easy it was to make. Luckily when I discovered this project, I knew were an old microwave was. I live in a small village in Guyana and most people here don't have microwaves. It was from a small restaurant. I successfully got the transformer out which was a little scary even for a 16 year old. I built a deluxe version of your design with the microwave light and fan incorporated in, along with four switches. My problem was that I didn't have any solid copper rod to use for the contacts. I had a few bronze welding rods so I used a small piece of that, instead. My welder is putting out about 1v. It melts nails and about anything else. I have not gotten it to actually weld. The metal to weld gets red hot but doesn't weld together. Any idea's whats wrong? I would appreciate any help. It's fun to melt metal, but it doesn't weld. Thanks.
Thanks for your comment! I'd love to see a little video of your welder as a video response to my video on YouTube, if you get a chance to do that?

It may help to press the contacts together harder when welding. You may also need more power. (Eg. Bigger transformer)
swolff12342 years ago
Yes, I am actually a ham. I got my license in Jan. No radio yet, but I have Echolink. I am getting my radio in March. Are you a ham? Thanks for all your help! BTW, the reply feature isn't working for me, I can only post new comments.
Sam Wolff KK4NVJ
The King of Random (author)  swolff12342 years ago
Awesome! I did get licensed but haven't ever done anything with it. I'm hoping that one day I can explore that world a little more :)
swolff12342 years ago
Found it! It was hiding from me..... Lol. Thanks again! Oh, how long does the trasformer last until the insulation on the 4 awg melts?
Best of luck,

Sam Wolff
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